Alkali metal perborates



Patented Dec. 2 0, 1949 ALKALI METAL PERBORATES James H. Young, Niagara Falls, N. Y., assignor to I. du; Pont do ,Nemours & Company, Wilmington, Del, a corporation of Delaware No Drawing. Application October 23, .1946, Serial No. 705,240

16 Claims. 1

This invention relates to solid compounds which contain peroxide or active oxygen. More particularly the invention relates to compounds of the type known as perb crates.

This application is a continuationin-part of my application, Serial No. 590,969, filed April 28, 1945 (now abandoned),

The usual method for producing perborates is to react solutions of borax, an alkali such as caustic or sodium peroxide, and hydrogen peroxide at low temperatures. Crystals of sodium perborate tetrahydrate separate because of low solubility in cold water. The product is dried to give the usual article of commerce which is 13330341320 or more probably NaBOz.H2Oz. 3HzO.

This so-called tetrahydrate contains about 10% of active oxygen. It softens and melts with concomitant decomposition at temperatures above about 40 C. it has been proposed to further dehydrate these tetrahydrate crystals to give the so-called monohydrate which chemically is NaBOsHzO or more probably NaBO2.H2O2. This product contains about of active oxygen. Dehydration of the tetrahydrate has not been an economical process because the low melting point of the tetrahydrate requires large volumes of air, the product dusts from the dryer, and decomposition losses are appreciable.

Since there are no absolutely stable peroxygen compounds it is very important to'produce compounds which, in storage, over a wide temperature range, show minimum losses of active oxygen.

An object of this invention is to provide a simple and inexpensive method for making perborates. Another object is to provide a method for preparing alkali metal per-borates having properties distinctly different from and markedly more desirable than those of perborates heretofore known. Still further objects will be apparent from the following description. fl

The above objects are accomplished in accordance with the invention by mixing at leastone boron compound from the group consisting of boric acids and alkali metal salts thereof with hydrogen peroxide-and an alkalisuch as an alkali metal peroxide or an alkali metal hydroxide, and sufiicient water to cause reaction to occur between the boron compound and the peroxide and to form a substantially homogeneous solution of the mixture at a reaction temperature in excess of at least 40 .C. and preferably not higher than about 60 C. After reaction, the solution is subected to rapid drying.

Experiments have shown that when carrying out the present method employing a reaction temperature as indicated above and when properly proportioning the reactants, there are obtained perborate products which differ markedly in properties from perborates prepared by prior methods and which are believed to be different structurally from prior products.

The sodium perborate tetrahydrate of commerce is usually prepared employing reactants in amounts corresponding to Na2O:Active OZB2O3 ratios of 1:211. The reaction is conventionally carried out at around 10 to 20 C. and the reaction mixture is then cooled still further .to crystallize out the product which is then air dried at temperatures below 40 0. (See Carveth U. S. Patent 1,716,874.) The crystalline product is only slightly soluble in cold water and dissolves relatively slowly. While fairly stable at ordinary temperatures, it is unstable at higher temperatures such as C.

Sodium perborate monohydrate prepared by dehydration of the tetrahydrate is a non-crystalline product which is somewhat more stable at 60 C. but resembles the tetrahydrate, to which it reverts, in the presence .of water. Previous attempts have been made to obtain a completely dehydrated product, but it was found that as dehydration progresses beyond the monohydrate stage oxygen is lost and a fundamental change in structure occurs whereby a product is formed which evolves gaseous oxygen instead of active oxygen when dissolved in water.

In contrast, the present improved products are non-crystalline and have a glassy appearance. In general they dissolve much more rapidly than .perborate tetrahydrate at ordinary temperatures and are much more soluble. They exhibit excellent stability even at 60 C. which is surprising since by the method of preparation all impurities in the raw materials are retained in the products since no separation by crystallization and filtration, which would have a purifying effect, is involved. The exact chemical structures have not been determined although analyses indicate that the present products probably are intimate mixtures or molecular combinations of compounds including NaBOaI-IzQz and NaBOs. Their noncrystalline, glassy appearance suggests that they are solid solutions. r

Throughout the specification and in the appended claims the proportions of starting materials are stated, unless specifically indicated otherwise, in terms of their total chemical equivalents of M20 (where M stands for .an alkali metal) or NazO, B203, H202 (or active oxygen) and H20. Likewise, the products are described in terms of 3 their total chemical equivalents of M20 or Na20, B203, H20 and active oxygen.

The present method may be practiced employing the reactants in proportions which may be varied considerably. Thus, the amounts of the reactants may be proportioned to correspond with NazozActive :13203 ratios of 1:2:1, as in the preparation of sodium perborate tetrahydrate by previous methods. stantial loss of active oxygen results due to the use of the higher reaction temperature which is characteristic of the present method. It is preferred that the reactants be proportioned so as to correspond to from 0.53 to 0.97 mole of Na20 per mole of B203 and from 0.5 to 2.5 atoms of active oxygen per mole of B203. When the reactants are so proportioned, the present improved products are obtained with high active oxygen recoveries.

The invention is further illustrated by the following examples:

Example 1 slowly flowing onto a drum dryer having stainless steel rolls. These rolls were heated at 20-25 lbs. steam pressure. The product on the rolls was at 124 C. The roll clearance was 0.007 to .009", and they were revolving at 4.5 R. P. M.

189 grams of a white'flaky product containing 15.97% active oxygen and showing a 95% recovery of the active oxygen put in was recovered.

After 6-8 months at 25-35 0., analysis of the product showed: 15.65% active oxygen, 15.03%

- H20 (including the H20 equivalent of any H202 present), 31.27% Na20 and 37.18% B203. The ratio of moles of H20 per atom of active oxygen was 0.855; the ratio of moles of Na20 per mole of B203 was 0.943; and the ratio of atoms of active oxygen per mole B203 was 1.83.

V Emample 2 A reaction was conducted as in Example 1 but without added sodium silicate. Drying was substantially the same.

187 grams of product containing 16.1% active oxygen and with a recovery of 94.8% of the active oxygen put in was recovered.

- After 6-8 months at 25-35 0., analysis of the product showed: 16.0% active oxygen, 14.66% H20, 31.15% Na20 and 37.70% B203. The ratio of moles of H20 per atom of active oxygen was 0.814; the ratio of moles of Na20 per mole of B203 was 0.930; and the ratio of atoms of active oxygen per mole of B203 was 1.85.

Ercample 3 The reaction was conducted as in Example 1 but with no added silicate.

The product was dried with the roll clearance at 0.004 to 0.005", roll temperature of 146 C. and

product temperature of 127 C. The time for drying the batch was 3 minutes. a r

In that case, however, subv lize out.

189 grams of product containing 16.03% active oxygen at 95.3% turnover was recovered.

After 6-8 months at -35 0., analysis of the product showed: 15.82% active oxygen, 15.34% H20, 31.54% Na20 and 37.20% B203. The ratio of moles of H20 per atom of active oxygen was 0.861; the ratio of moles of Na20 per mole of B203 was 0.953; and the ratio of atoms of active oxygen per mole of B203 was 1.85.

Example 4 190.5 grams of borax decahydrate (0.5 mole) was added slowly to 79.4 ml. of 130 vol. hydrogen peroxide (0.92 mole H202) with good stirring. 8 grams solid sodium peroxide (0.12 mole) was added slowly with cooling to maintain a temperature of not over 50 C. The mixture was stirred one hour. It was then poured over the rolls of a drum dryer heated with 16 lbs. steam.

138 grams of product containing 10.8% active oxygen with a recovery of 91% of the active oxygen was obtained.

Example 5 381 grams of borax decahydrate (1 mole) was mixed with 64 grams of solid sodium peroxide (0.82 mole) and added to 300 grams of 130 vol. hydrogen peroxide (3 moles H202) and the mixture processed as in Example 1.

353 grams of product containing 16.63% active oxygen and showing a 94.8% recovery of active oxygen was obtained.

Example 6 A mixture of 469.5 lbs. of borax and 87.5 lbs. of sodium peroxide together with 391.5 lbs.'of 130 vol. hydrogen peroxide was fed continuously into a stirred and jacketed stainless steel reaction vessel maintained at 46-50 C. The solution was continuously overfiowed onto a 2 roll drum dryer having cast iron rolls maintained at 145-150 0. Analysis of the product indicated a recovery of about 93% based on active oxygen input.

A sample of the product obtained during the above run analyzed 18.69% active oxygen, 13.85% H20, 30.18% Na20 and 36.88% B203. The ratio of moles of H20 per atom of active oxygen was 0.66; the ratio of moles of Na20 per mole of B203 was 0.919; and the ratio of atoms of active oxygen per mole of B203 was 2.21.

Example 7 By similar processing and by suitably adjusting the ratios of H202 to borax and sodium peroxide, compositions containing 17.27, 18.60, 19.22 and 20.67% active oxygen were made. Recoveries and stabilities were good.

The reaction should be carried out at a temperature of at least 40 C. and preferably not over 60 C. At higher temperatures, recovery of active oxygen is poor and at lower temperatures perborate tetrahydrate tends to form and crystal- The preferred temperature is to C. The temperature employed will depend to some extent upon the amount of total water (including water of crystallization and the water equivalent of hydrogen peroxide) present in the mixture as well as upon the rate at which the mixture after completion of the reaction is transferred to the dryer. In all cases, the substantially homogeneous reaction solution should be maintained at such a temperature as will avoid crystallization prior to evaporation.

Suitable boron compounds for use are orthoand pyroboric acids, boric anhydride (B203) and 'l prefer to employan alkalimetal peroxidersuch as sodium peroxide as the required alkali, since such a compound :will also supply part of the active oxygen requirements. However, the invention may be practiced successfully "employing "only an alkali metal hydroxide, in whicheven't larger quantities of hydrogen peroxide will be used: 7

It is preferred to so proportion the reactants that the reaction mixture will contain theequivalent of 0.53 to 0.97 mole of M20 (M stands for an alkali metal) per mole-o'f B203, including the 'MZO-and Bzosequivailents of all alkali metal and all boron compounds used. Best results are achieved using reactant proportions correspond-- in; toOi8 to-ofiamdle of 1v i2o'- e'r mole of B203.

The amount of active oXy'g'n added to the reaction mixture, eitheras hydrogen peroxide or as alkali metal peroxide,maybe 'varied Widely. However, if the active'oxy'gen used is equivalent to less "than about 05 atom per mole oi B203, the resulting product will contain such a 'loW concentration offabti ve OXYgh that it will be of little 'Valll commercially. Use of the equivalent of from 0.5 1702.5"a tomsoi active oxygen per 'mole of B: is recommendedand b'est results are obtained when using from 1.8 to "22 atoms per'mo'le of B203.

As stated previously there should be sufficient water present in the reaction mixture to cause the reaction to occur and to form a homogeneous 'solutionat the'des'ired reaction temperature. An excess of water 'is not particularly harmful except that morewater must be evaporated in obtaining the final dry product. Reaction mixtures con taining total water (includingwa'ter of 'crysta'i lization and the water equivalent of H202, assuming complete decomposition according to the Equation: 2H2Oz* 2H2O-FO2) equiva1entt 7.5 to "60 moles per'mole of B203 may be used although mixtures containing from '8 tom moles of water per mole of B20: are preferred.

M The process of the invention represents a distinc't advance over the 'prior artin that the ratio of alkali -to B203 "and of active oxygen 130E203 the 'fin'al product -can be regulated as desired. lllhefofasformerly,theproduct was recovered from so ution by crystallization at low temperatures,

:glasfs'y a1p'earing products. "Ifhey are outstandin'giy "more "stable than sodium enetrate tctr a- {hydrate 6i mbnfiliyiiiate, *part'i'cuiptny at-levatei temperatures; are much more soluble in water; and dissolve at a more 'rapidrate. Theiractive oxygen contents will --correspona roughly to the amount-of active oxygenemployed in their preparation. Productscontaining 0ver'20% by weight of active oxygen may be obtained but those having 15 to about 17% eret'rererred. As the a'ctive oxygen content isfincieaseizl above about 11%, sdlubilitytends t'o dec rease and above'a-bout 22% "stability decreases somewhat although products containingsuch'high aotiveoxygen content can be Obtained ina'cCOrfiaflCevvith the invent-ion.

The dried products, of course, contain some water present "itli'r B's 'Wat'l "of crystallization "OT as hydrogehperoxide'of crystallization. In general the water content, including'th'e H2O equivalent of any chemically bound H202, will be not higher than about 2 moles of water per atom of active x'ygen present. in rno's't (if the products, there be flofii 054 1'10 B05 m'ole's (if total W t'l per atom of active tix yigel l Profit-ibis containing more than about 15% acuve'bxy'gen will, ivhen thoroughly dry, contain substantially less than 1 r'noleof Water, e. -'g., riot more than flfimolefiper gram atom of active dxygen.

The ratio dfjMG to -H203 ill the firdlict vfill, o'f-cours'efbe the 'safn'e-asih therea'c'tio'n mixture since the dry product is obtained by "evaporation 'toiiryne ss of the-resentin-measure.

The rii is exothermic 'and cooling should g lihe i ea ctant's. I

Inbrder to 'economiz bn the 'cost of -removing water, it is preferable to use relatively concenea e solutions or hydrogen peroxide. The socall'ed 130 voluine hydrog'enperoxide of co'mrnerce which contains about H202 by weight is satisfactory. Hydrogen peroxide solutions which Contain between 25% "and T1202 Can "be In order to mcrease"stabilityin storage and in "solution, small amounrser sodium pyrophosphate '(Nar'PiOv) or or sodium silicate and magnesium sulfate maybeaddedas stabilizers. For'example, 1.0% "sodium pyrophosp'hate'tir 0.5% sodium silicate with 0.2% magnesiumsulfa'te maybe added to the hydrogen peroxidebefore adding theb'o'rax andsodium peroxide. Useof 'su'ch stabilizers is iparticularly advantageous when 'preparin'gprod- "ucts which arenotfthorouglilvdriedor product's 'containinghigh'active oxy en content.

It lsdesirabletoprevent'the system from becoming too alkaline at any stage of'the process. J'Ihis may be accomplish {by "first adding the l'aorax tothehydro'gen"peroxide solution and then adding the sodium jperoxide. The b'orax and "Sodium peroxide 'lh'afy 'be fed siinu-ltahous ly. AIl three reactants maybe-fed "continuously and the reaction mixture continuously withdrawn and ilrie'd. 7 e 7 'As with practically all;peroxides, heavy metal contamination is undesirable. Suitable reactors may be Stainless s't-elflglass, ceramic ware, or enameled'm'etal.

After the "reaction isfco'inplete and all reactants are in solution, the slightly viscous,-syrup-like solution 'is flowed ont'oia "dryer, prefer-ably having cast iron,'s'tainless steel or chromeplated rolls. The temperatureof the rolls may be about to 0. depending upon the speed of roll rotation and how "fast; product is being fiowed on the rolls. 4 If'thoroughly dry a White flak-y procl-- uct -is removed. Eartlydry products are l more or "less.gpastyangl sticky. Eather complete dryingH-is necessary to obtain a product of maximum storage Per Cent of Orig. Act. Ratio Moles Sample Content 11 0: Atoms Per Cent Act. 0 Weeks Even the least stable of the above products is markedly more stable than ordinary sodium perborate tetrahydrate or the monohydrateprepared therefrom as is shown below.

The drying temperature may, of course, be lowered considerably by drying under reduced pressure. However, use of a drum dryer at atmospheric pressure with the drying surfaces at a temperature of 100 to 150 C. is very practical and preferred. Rapid drying is desired, particularly when using drying surfaces at a temperature above about 100 C. Employing such temperatures, best results are achieved when drying (i. e., removal of substantially all water not present as combined water or hydrogen peroxide of crystallization) is accomplished within 2-3 minutes and preferably less than 1 minute. At lower temperatures, e. g., at 60 to 100 0., longer drying times are possible but in general should not exceed about one hour. Spray drying may be employed, thus the solution of the reaction mixture may be contacted in finely divided form with a stream of dry heated air. For example, the solution may be sprayed into a stream of dry hot air whereby finely divided solid dry particles are rapidly formed and may be recovered 7 from the air stream by known means.

Isolation of the product is accomplished by the continued application of heat to the syrup-like solution of reaction products until evaporation of water therefrom as a result of the heat applied leaves the product in the form of a dry residue. As stated previously, evaporation at a temperature above the boiling point of water is preferred and rapid drying may be readily accomplished with excellent results at atmosphere pressure by the use of a drum dryer whose drying surfaces are maintained at a temperature above 100 C. but not exceeding about 150 C.

It is not possible to dissolve more than about 4 parts of the ordinary sodium perborate tetrahydrate of commerce, as prepared by the method of Carveth U. S. Patent 1,716,874, in 100 parts of water at 30 C. Sodium perborate monohydrate prepared from the above tetrahydrate by dehydration in a rotary dryer at a temperature beginning at about 40 C. and rising to 90 C., rapidly reverts to the tetrahydrate upon the addition of water and then behaves as the tetrahydrate.

In contrast, the present preferred products, for example, those of Examples 1, 2 and 3, readily dissolve completely in 1.5 to 3 times their weight 7 an hour or more, gradually deposit sodium perborate tetrahydrate to give a solid mass of moist crystals. The transition from the products of this invention to perborate tetrahydrate is accompanied by a very considerable heat evolution showing a very definite chemical change.

The following table shows the relative stability of the products of this invention and of perborate tetrahydrate and monohydrate produced by former methods.

Per Cent of Orig. Act. 0 Lost at AOrtigb 60 C. in-- c Product Content Per Cent 2-5 7 12 16 Days Weeks Weeks Weeks Perborate Tetrahyrate Perborate Monohydrate Product of Example 1.

Product of Example 2. Product of Example 3.

1 This loss was in 6 weeks.

The "perborate tetrahydrate of the above table was taken from a commercial lot of sodium perborate tetrahydrate prepared by the process described in Carveth U. S. Patent 1,716,874. The perborate monohydrate was made from the above perborate tetrahydrate by dehydration in a conventional rotary dryer at a temperature beginning at about 40 C. and rising to C.

The perborate products obtained in accordance with the present invention are useful in bleaching, in soap powders, in dentifrices and for various other purposes- The high active oxygen content and excellent stability of the present improved products represent distinct advances over former compositions. The simplified processing renders the product less expensive and hence more widely useful.

Iclaim:

l. A process for the production of an alkali metal perborate product comprising mixing a boron compound from the group consisting of and applying heat so as to evaporate water from said homogeneous solution and leave as a residue a solid alkali metal perborate product.

2. A process for the production of an alkali metal perborate product comprising mixing together an alkali metal tetraborate, hydrogen peroxide, and an alkali from the group consisting of the alkali metal peroxides and hydroxides with sufiicient water to cause reaction to occur between said boron compound, hydrogen peroxide and alkali and to form a substantially homogeneous solution of the resulting mixture and applying heat so as to evaporate water from said homogeneous solution and leave as aresidue a solid alkali metal perborate product.

peroxide, and an alkali from the group consisting of the alkali metal peroxides and hydroxides with suflicient water to cause reaction to occur between said boron compound, hydrogen peroxide and alkali and to form a substantially homogeneuos solution of the resulting mixture and evaporating water from said homogeneous solution at a temperature above the boiling of water to leave as a residue 2. solid alkali metal perborate product.

4. A process for the production of an alkali metal perborate product comprising mixing together a sodium tetraborate, hydrogen peroxide, and an alkali from the group consisting of sodium peroxide and sodium hydroxide with sufficient water to cause reaction to occur between said boron compound, hydrogen peroxide and alkali and to form a substantially homogeneous solution of the resulting mixture and applying heat so as to evaporate water from said homogeneous solution and leave as a residue a solid sodium perborate product.

5. A process for the production of an alkali perborate product comprising reacting at a temperature of 40-60 C. a boron compound of the group consisting of boric acid and the alkali metal salts thereof with hydrogen peroxide and an alkali from the group consisting of the alkali metal peroxides and hydroxides in the presence of sufficient water to form a homogeneous solution of the reaction mixture, said reactants being so proportioned that there are present in the reaction mixture the equivalent of from 0.53 to 0.97 mole of M20, M standing for an alkali metal, and from 0.5 to 2.5 atoms of active oxygen per mole of B203, and evaporating Water at a temperature above the boiling point of water from the resulting homogeneous solution of reaction product to leave as a residue a solid alkali metal perborate product.

6. The method of claim 5, wherein the reactants are a sodium tetraborate, hydrogen peroxide and sodium peroxide.

7. A process for the production of a sodium perborate product comprising reacting together a sodium tetraborate, hydrogen peroxide and sodium peroxide at a temperature of 4060 C. in the presence of water, said reactants and Water being present in the reaction mixture in amounts equivalent to 0.53 to 0.97 mole of NazO, 0.5 to 2.5 atoms of active oxygen and 7.5 to 60 moles of water per mole of B203, and evaporating water at a temperature above the boiling point of water from the resulting homogeneous solution of reaction product to leave as a residue a solid sodium perborate product.

8. A process for the production of a sodium perborate product comprising reacting together a sodium tetraborate, hydrogen peroxide and sodium peroxide at a temperature of 40-60 C. in the presence of water, said reactants and water being present in the reaction mixture in amounts equivalent to 0.8 to 0.95 mole of NazO, 1.8 to 2.2 atoms of active oxygen and 7.5 to 60 moles of water per mole of B203, and evaporating water at a temperature above the boiling point of water from the resulting homogeneous solution of reaction product to leave as a residue a solid sodium perborate product.

9. A process for the production of a sodium perborate product comprising reacting together a sodium tetraborate, hydrogen peroxide and sodium peroxide at a temperature of 45-55 C. in the presence of water, said reactants and water being present in the reaction mixture in amounts equivalent to 0.8 to 0.95 mole of NazO, 1.8 to 2.2 atoms active oxygen and 8 to 12 moles of water per mole of B203, and evaporating the resulting homogeneous solution of reaction product from a surface having a temperature of -150 C. to leave as a residue a solid sodium perborate prodnot.

10. A solid alkali metal perborate product each particle of which is non-crystalline and contains in combined form 0.53 to 0.97 mole of alkali metal oxide and 0.5 to 2.5 atoms of active oxygen per mole of 13203 and not more than 2 moles of combined water per atom of combined active oxygen.

11. A solid sodium perborate product each particle of which is non-crystalline and contains in combined form 0.53 to 0.97 mole of NazO and 1.8 to 2.2 atoms of active oxygen per mole of B20: and not more than 2 moles of combined water per atom of combined active oxygen.

12. A solid sodium perborate product each particle of which is non-crystalline and contains in combined form 0.8 to 0.95 mole of NazO and 1.8 to 2.2 atoms of active oxygen per mole of B20: and not more than 2 moles of combined water per atom of combined active ox en.

13. A solid sodium perborate product each particle of which is non-crystalline and contains in combined form 0.53 to 0.97 mole NazO and 0.5 to 2.5 atoms of active oxygen per mole of B20; and not more than 2 moles of combined water per atom of combined active oxygen.

14. A solid sodium perborate product each particle of which is non-crystalline and contains in combined form 0.8 to 0.95 mole of NazO and 1.8 to 2.2 atoms of active oxygen per mole of B20: and from 0.4. to 1.05 moles of combined water per atom of combined active oxygen.

15. A solid non-crystalline sodium perborate having an active oxygen content of at least 15% by weight and less than one mole of combined water per atom of combined active oxygen.

16. A solid sodium perborate each particle of which is non-crystalline and contains in combined form 0.8 to 0.95 mole of NazO per mole of B203 and less than 1 mole of water per atom of active oxygen, has an active oxygen content of 15 to 17% by weight and is completely soluble at 30 C. in 1.5 to 3 times its weight of water.

JAMES H. YOUNG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 903,967 Fritsche Nov. 17, 1908 1,677,283 Jones July 17, 1928 1,716,874 Carveth June 11, 1929 2,065,744 Reichert Dec. 29, 1936 2,380,779 Nees July 31, 1945 

